Those projects (Blues Brotehr and Hudson Hawk) were started with the goal to use the Moktar/Titus the Fox engine.
The problems when modifying a fully working engine/game :
--may be some slight difference in gameplay...who may be hard to code or add.
--You may need Graphists or Musicians...as a coder is not always good at those.
--You try to understand the programm from scratch, because you didn't wrote it...
--this remains time consuming.
Exemple :
--Blues Brother : the ballons or umbrella may be hard to add...
It think it would be great if Amstrad 8 bit community worked on efficiant generic action games engines.
By generic, I mean easy to mod, because we would have all design explanations et explainned blueprints, and so on...
Because it would be the work of a community, not a lone coder.
Also, the best games engines should be decrypted and fully analysed, those ressources then put in common.
It always looks like you have to start from zero again each time you want to make a project...